Alkylated aromatic diisocyanates have been known for a substantial period of time and find use in the preparation of polyurethane and polyurea elastomers. The isocyanates are reacted with polyols to produce a polyurethane sysem which then can be crosslinked with an aromatic diamine to form a polyurethane/urea elastomer or crosslinked with a short chained diol or triol to produce polyurethane elastomers. Alkylated and substituted aromatic isocyanates which have found use in preparing various elastomer systems are noted in the following patents:
British Pat. No. 1,080,739 discloses alkylated mononuclear monoisocyanates and alkylated diphenyldiisocyanates. The isocyanates are characterized as containing a tertiary alkyl group in ortho positions to each isocyanate group to inhibit the reactivity of the isocyanate group. The reduced reactivity permits greater flexibility in carrying out reactions and the utilization of wider variety of reactants for producing elastomer systems. Examples of diphenylmethanediisocyanates having hindered groups include the isocyanate derivatives of 4,4'-methylene bis(2-tert-butylaniline) and 4,4'-methylene bis(2-methyl-6-tert-butylaniline).
U.S. Pat. No. 3,105,845 discloses the preparation of tetraalkylated mononuclear aromatic polyisocyanates and their use in producing a variety of elastomeric systems. One of the advantages of the alkylated mononuclear aromatic isocyanates is in their reduced reactivity and thus provides a more stable "pot life" for polymer intermediates. Examples of diisocyanates include 1,3,5-trimethyl-2,4-disocyanatobenzene; durene isocyanate and 1,3-dimethyl-2,5-diethyl-4,6-diisocyanatobenzene.
U.S. Pat. No. 4,399,073 discloses a process for producing tertiary alkyl isocyanates such as tetramethylxylenediisocyanate, 1,3,5-tris(1-isocyanato-1-methylethyl)benzene and .alpha.,.alpha.-dimethyl-4-isopropenylbenzeneisocyanate.
U.S. Pat. No. 3,878,235 discloses the production of chlorine-containing methylene-bridged diaryl diisocyanates and the use of these diisocyanates for the preparation of polyurethane elastomer systems. The chloro containing methylene bridged diphenyldiisocyanates have low viscosity and low volatility as compared to toluenediisocyanate for example thus reducing the toxicity problem associated with a mononuclear aromatic diisocyanate such as toluenediisocyanate. The ortho-chlorobenzyltoluenediisocyanate was shown to be a stable liquid under extended period of time as whereas the para-chlorobenzyl-toluenediisocyanate was not a stable liquid but exhibited partial solidification on standing.
U.S. Pat. No. 3,180,883 discloses 4,4'-diisocyanato-3,5-di-lower alkyl diphenylmethane compositions for use in preparing polyurethanes. Blocking groups are disclosed which inhibit the reactivity of one of the isocyanate groups, these blocking groups being halogen or alkyl.